This invention uses the multiple transponder response repetition interval (RRI) variation and elements of the coherent signal processing of my application Ser. No. 7/850,423 filed Mar. 12, 1992 and issued as U.S. Pat. No. 5,264,854 on Nov. 23, 1993. It uses the coherent detection means for offset frequency vehicle mounted transponders and elements of the associated skin return of transponder and non-transponder equipped vehicles of my copending application Ser. No. 07/941,716 filed Sep. 8, 1992.